Bonding method of small parts and module of combined small parts

ABSTRACT

A groove ( 3 ) having a V-shaped section is provided on a bonding surface ( 1   a ) of an IC chip ( 1 ) being as a first small part, while an elongate projection ( 4 ) having a V-shaped section to engage with the groove ( 3 ) of the first IC chip ( 1 ) is provided on a corresponding portion of a bonding surface ( 2   a ) of an IC chip ( 2 ) being as a second small part ( 2 ). Then, the IC chips ( 1, 2 ) are bonded together by the action of a holding force resulting from fitting the elongate protection ( 4 ) of the second IC chip to the groove ( 3 ) of the first IC chip ( 1 ), together with a bonding force produced between the bonding surfaces by interatomic force and metallic bond.

TECHNICAL FIELD

[0001] This invention relates to a bonding method of small parts such asLSI or like semiconductor parts, semiconductor devices and IC chipsserving as elemental parts of a micromachine, and a module of combinedsmall parts formed by bonding these small parts together.

RELATED ART

[0002] A machine of mm order such as a micromachine composed of aplurality of small parts has been developed. The small parts include ICchips or the like, for instance, and the machine such as themicromachine is assembled by bonding the IC chips together.

[0003] The problems arising when bonding the IC chips together arepositioning accuracy of small parts to be bonded together, dimensionaldispersion caused by the film thickness of an adhesive applied betweenthe small parts and the deficiency in bonding strength resulting frominsufficient bonding area.

[0004] As a method for obtaing a sufficient bonding strength in bondingsmall parts together, a hydrogen-bond applied technique is known, inwhich silicon wafers, each having a bonding surface subjected to surfacehydrophilic treatment (absorption of OH group) is treated with heat of atemperature of not less than 1000° C. under no pressure to form asurface oxidized layer, and the silicon wafers are bonded togetherthrough the surface oxidized layers. However, since the bonding has tobe made under the extreme environment, it is difficult to use anequipment for positioning of the parts, thereby causing problems suchthat necessary positioning accuracy cannot be assured and that alarge-scaled apparatus is needed for heat treatment.

[0005] When electrical connections among the small parts such as ICchips are required, an input/output contact of an IC chip molded withepoxy resin is led outside through a lead frame, a leg of the lead frameis mounted on a substrate and this IC chip is connected with another ICchip mounted on the substrate in the same manner through printed wiringon the substrate. Recently, a multi-chip module or the like is known, inwhich a plurality of chips arranged on an alumina substrate areconnected together through thin-film copper wiring of about 20 micronsin conductor spacing. However, in either case, the connection betweenthe chips requires the wiring, and this wiring has been a majorhindrance to higher speed and higher integration of a circuit.

[0006] According to the recent technique, the width or conductor spacingof sub-micron order is practically available for the wiring produced bya semiconductor process in a chip. However, an interface portionrequired for the electrical connection between the chips, for instance,connecting portions of the leg of the lead frame and the copper wiring,still requires a considerably large contact area as compared with thewidth or conductor spacing of the wiring produced by the semiconductorprocess, being factors of hindrance to higher integration of thecircuit. To be more specific, the spacing between contacts is about 200microns with the wiring width of 30 microns in the case where contactconnection of wire bonding type is applied, while the spacing betweencontacts is about 80 microns with the wiring width of 30 microns in thecase where contact connection of flip chip bonding type is applied.

DISCLOSURE OF THE INVENTION

[0007] It is an object of the present invention to provide a bondingmethod of small parts and a module of combined small parts formed bybonding the small parts together, wherein slight bonding areas on thesmall parts suffice to exert a satisfactory bonding strength withoutneed of any adhesive, complicated chemical processing and heattreatments, but the small parts can be bonded together with highpositioning accuracy to obtain a circuit of higher speed and higherintegration.

[0008] According to the present invention, a first small part and asecond small part are bonded together by means of one or two or moreV-shaped grooves formed on a bonding surface of the first small part,and grooves V-shaped elongate projections, which are engageable with theV-shaped grooves, on a bonding surface of the second small part, therebyfitting the V-shaped elongate projections of the second small part tothe V-shaped grooves of the first small part.

[0009] According to the present invention, the small parts can be bondedtogether with a sufficient strength without requiring any adhesive,complicated chemical processing and heat treatments, and the degree ofthe strength of the bonded state of the small parts can be determinedselectively at will if occasion demands. Moreover, since the elongateprojection and the tapered groove are joined by being fitted with eachother, the positioning accuracy in bonding the small parts together canalso be assured.

[0010] Further, since the tapered groove and the elongate projectionserving as bonding portions of the small parts are provided withelectrical contacts for transfer of signals between the objects to bebonded together to electrically connect the small parts together, anyintermediate connecting means such as a lead frame, printed wiring andcopper wiring becomes unnecessary, thereby making it possible not onlyto obtain at a circuit of higher speed but also to prevent theinevitable increase in the size of the node at a portion of connectionbetween the contact and the wiring, contributing to higher integrationof the circuit too.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1A is a perspective view showing a first IC chip having oneV-shaped groove, together with a second IC chip having one V-shapedelongate projection;

[0012]FIG. 1B is a perspective view showing the state in which the firstIC chip and the second IC chip bonded together by fitting the V-shapedgroove of the first IC chip shown in FIG. 1A to the V-shaped elongateprojection of the second IC chip shown in FIG. 1A according to a methodof the present invention;

[0013]FIG. 2A is a perspective view showing a first IC chip having twoV-shaped grooves in different directions, together with a second IC chiphaving two V-shaped elongate projections in different directions;

[0014]FIG. 2B is a perspective view showing the state in which the firstIC chip and the second IC chip are bonded together by fitting theV-shaped grooves of the first IC chip shown in FIG. 2A to the V-shapedelongate projections of the second IC chip shown in FIG. 2A according toa method of the present invention;

[0015]FIG. 3A is a perspective view showing a first IC chip having alarge number of V-shaped grooves parallel to one another, together witha second IC chip having a large number of V-shaped elongate projectionsparallel to one another;

[0016]FIG. 3B is a perspective view showing the state in which the firstIC chip and the second IC chip are bonded together by fitting the largenumber of V-shaped grooves of the first IC chip shown in FIG. 3A to thelarge number of V-shaped elongate projections of the second IC chipshown in FIG. 3A according to a method of the present invention;

[0017]FIG. 4A is a perspective view showing a first IC chip having alarge number of V-shaped grooves parallel to one another in a firstdirection and a large number of V-shaped grooves in a second directiondifferent from the first direction, together with a second IC chiphaving a large number of V-shaped elongate projections parallel to oneanother in a first direction and a large number of V-shaped elongateprojections in a second direction different from the first direction;

[0018]FIG. 4B is a perspective view showing the state in which the firstIC chip and the second IC chip are bonded together by fitting the largenumber of V-shaped grooves of the first IC chip shown in FIG. 4A to thelarge number of V-shaped elongate projections of the second IC chipshown in FIG. 4A according to a method of the present invention;

[0019]FIG. 5 is a perspective view showing a case where a plurality ofIC chips can be bonded to the front and rear of one IC chip according toa method of the present invention;

[0020]FIG. 6A is a view for explaining a case where a first IC chip anda second IC chip are placed not allowing to be detached from each other,since, when a plurality of V-shaped grooves formed on the first IC chipare engaged with a plurality of V-shaped elongate projections formed onthe second IC chip, angle a of V-shaped elongate projections and also ofV-shaped grooves is small;

[0021]FIG. 6B is a view for explaining a case where a first IC chip anda second IC chip, engaged with each other, can be detached from eachother when external force is applied, since, when a plurality ofV-shaped grooves formed on the first IC chip are engaged with aplurality of V-shaped elongate projections formed on the second IC chip,angle αof V-shaped elongate projections and also of V-shaped grooves isslightly large;

[0022]FIG. 6C is a view for explaining a case where a first IC chip canslide relative to a second IC chip, since, when a plurality of V-shapedgrooves formed on the first IC chip are engaged with a plurality ofV-shaped elongate projections formed on the second IC chip, angle α ofV-shaped elongate projections and also of V-shaped grooves isconsiderably large.

[0023]FIG. 7 is a view for explaining a case where contacts are locallyformed on parts of oblique walls of a V-shaped groove of an IC chip anda belt-shaped contact is formed covering both the oblique wall and anadjoining bonding surface.

BEST MODE OF EMBODYING THE INVENTION

[0024] Hereinafter described is an embodiment of a bonding method ofsmall parts according to the present invention which is applied tobonding of IC chips serving as elemental parts of a micromachine. Themicromachine is considered to be a machine composed of elemental partshaving size in the range from about 1 μm to 1 mm.

[0025] Incidentally, the small parts mentioned in the description of thepresent invention include parts such as LSI or like semiconductor partsand semiconductor devices, in addition to IC chips constituting amicromachine. These small parts normally include parts having size ofsubmillimeters to mill meters, or may also include parts having sizelarger than the above.

[0026]FIGS. 1A and 1B show an embodiment in which two IC chips 1 and 2of rectangular parallelepiped shape are bonded together by means offitting an elongate projection into a tapered groove.

[0027] As shown in FIG. 1A, a tapered groove 3 having a V-shaped sectionis provided in the center of a bonding surface 1 a of one IC chip 1,while an elongate projection 4 having a V-shaped section is provided asone body in the center of a bonding surface 2 a of the other IC chip 2and has tapered surfaces 4 a and 4 b to be fitted with two walls 3 a and3 b of the tapered groove 3.

[0028] In the embodiment shown in FIG. 1A, since the IC chip 2 has arelatively small thickness, the tapered groove 3 is provided on the sideof the bonding surface 1 a of the IC chip 1 , while the elongateprojection 4 is provided on the side of the bonding surface 2 a of theIC chip 2. However, when the IC chip 2 has a sufficient thickness, thetapered groove 3 may be provided on the side of the bonding surface 2 aof the IC chip 2, while the elongate projection 4 may be provided on theside of the bonding surface 1 a of the IC chip 1.

[0029] The appropriate depth of the tapered groove 3 is about 1 to 10microns, or may be larger if circumstances require, and therefore, maybe selectively determined according to the accuracy and the quality ofmaterial of the IC chips 1 and 2 for bonding and bonding strengthrequired or the like. The depth of the tapered groove 3 and the heightof the elongate projection 4 are micro-millimeters, and the two walls 3a and 3 b of the tapered groove 3, the tapered surfaces 4 a and 4 b ofthe elongate projection 4 and the bonding surfaces 1 a and 2 a have tobe finished with higher degree of accuracy or surface roughness (thatis, with mirror finishing of Rmax not exceeding 0.1 μm).

[0030] Machining such as shaping and milling by the use of a singlecrystalline diamond tool together with a super-precision machine isknown as a method of mechanically forming V-shaped grooves with such ahigh accuracy. According to this method, although depending on theaccuracy of a machine, V-shaped grooves at a pitch of about 1 micron aremachined accurately enough to attain the surface roughness of about 10nm in Rmax, so that it is possible to flexibly cope with a difference inmaterial of the micro part, which is an object to be machined, to acertain degree. Further, if machining with a machine and a tool eachcarefully selected is carried out, it is possible to obtain any depth ortapered angle of the tapered groove 3, and the elongate projection 4 tosome degree. However, this method is not always suited for massproduction of products because the high-degree positioning work andprecise dressing work is required in machining.

[0031] Anisotropic etching by the use of KOH is known as a method offorming the highly-accurate V-shaped grooves according to chemicaltreatment. This anisotropic etching is used for producing an accurateV-shaped groove of 70.5° on 1-0-0 wafer coated with a rectangular mask,by making use of etching speed lag of 1-1-1 surface which is caused byanisotropy when applying etching treatment with KOH to singlecrystalline silicon. Therefore, mass production of small parts providedwith V-shaped grooves having an accurate taper angle is possibleprovided that an appropriate mask is available. However, the anisotropicetching described above has a disadvantage in that the V-shaped groovesunconditionally have a fixed angle of 70.5° and that a material of asmall part has to be one consisting of single crystalline silicon.

[0032] As shown in FIG. 1B, the IC chip 1 and the IC chip 2 are bondedtogether by inserting the elongate projection 4 of the IC chip 2 intothe tapered groove 3 of the IC chip 1 and causing the two walls 3 a and3 b of the tapered groove 3 to pinch the tapered surfaces 4 a and 4 b ofthe elongate projection 4. Since friction is produced between the twowalls 3 a and 3 b and the tapered surfaces 4 a and 4 b, the IC chip 1and the IC chip 2 are bonded together by the action of pinching force.In this case, the bonding of the IC chips is based on a wedge effect,and therefore, a description will now be given on the wedge effect inthe following.

[0033] When the elongate projection 4 of the IC chip 2 is pressedagainst the tapered groove 3 of the IC chip 1 with a certain force F,the IC chip 1 and the IC chip 2 are elastically deformed, causing aforce N to be produced in a direction perpendicular to the taperedsurfaces 4 a and 4 b of the elongate projection 4 (and the two walls 3 aand 3 b of the tapered groove 3). As a result, a frictional force Kproportional to the force N and the coefficient μ of the friction isproduced between the tapered surfaces 4 a and 4 b of the elongateprojection 4 and the two walls 3 a and 3 b of the tapered groove 3bonded to the elongate projection. The effect of this frictional force Kon the bonding of the IC chip 1 to the IC chip 2 is called the wedgeeffect. Incidentally, the wedge effect is not only proportional to thepress force F and the coefficient μ of friction, but also depends on anangle α (See FIGS. 6A to 6C ) of the tapered surfaces 4 a and 4 b of theelongate projection 4 (and that of the two walls 3 a and 3 b of thetapered groove 3).

[0034] Since the tapered surfaces 4 a and 4 b of the elongate projection4 are pressed very accurately against the two walls 3 a and 3 b of thetapered groove 3, a bonding force resulting from an interatomic forceand metallic bond is produced between the bonding surfaces, in additionto the bonding force based on the wedge effect mentioned above, therebyproviding a greater bonding force, compared with that in case of thebonding using only the wedge effects.

[0035] Further, since no adhesive has to be used, there is no chance ofthe dimensional dispersion caused by an adhesive layer interposedbetween the IC chip 1 and the IC chip 2. Moreover, since the bondingwork is carried out at room temperature, it is possible to use a precisepositioning device when bonding the IC chip 1 and the IC chip 2together. Further, since the tapered groove 3 of the IC chip 1 and theelongate projection 4 of the IC chip 2 are used as guides for the finalpositioning, the IC chips can be positioned with a high accuracy atleast in one direction within a horizontal plane.

[0036] When more accurate positioning is required for the bonding of theIC chip 1 to the IC chip 2, two kinds of tapered grooves, such astapered grooves 3 and 5 different in directivity from each other, areformed on the bonding surface 1 a of one IC chip, that is, the IC chip1, for instance, while elongate projections 4 and 6 respectivelycorresponding to the tapered grooves 3 and 5 are formed on the bondingsurface 2 a of the other IC chip, that is, the IC chip2, as shown inFIG. 2A.

[0037] Since the positional relation between the IC chip 1 and the ICchip 2 of FIG. 2A is unconditionally determined according to the taperedgrooves 3 and 5 and the elongate projections 4 and 6 respectivelylocated on two straight lines which are not parallel to each other, asshown in FIG. 2B, the positioning work in bonding the both together canbe carried out with accuracy to a higher degree. Since the positionalaccuracy in bonding the IC chip 1 to the IC chip 2 is dependent on themachining accuracy of the tapered grooves 3 and 5 and the elongateprojections 4 and 6, the strict accuracy is required for the machiningof the tapered grooves 3 and 5 and the elongate projections 4 and 6.

[0038] In the embodiment shown in FIG. 2A, the tapered grooves 3 and 5and their corresponding elongate projections 4 and 6 are provided atright angles with each other. However, it is to be understood that thetapered grooves 3 and 5 and the elongate projections 4 and 6 may beprovided at angles other than the right angles. Further, it is notalways necessary to provide the tapered grooves 3 and 5 and the elongateprojections 4 and 6 intersecting each other at one place overapping witheach other, as shown in FIG. 2A

[0039] Since the bonding force based on the wedge effect is producedbetween the tapered groove 5 and the elongate projection 6, in additionto the bonding force produced between the tapered groove 3 and theelongate projection 4, it is possible to achieve the more firm bondingas compared with the embodiment shown in FIGS. 1A and 1B.

[0040] When it is necessary to increase the bonding strength between theIC chip 1 and the IC chip 2, a plurality of tapered grooves 3 may beprovided in rows on the bonding surface 1 a of the IC chip 1, while aplurality of elongate projections 4 respectively corresponding to thetapered grooves 3 are provided in rows on the bonding surface 2 a of theIC chip 2, thereby increasing a substantial area of fitting between thetapered grooves 3 and the elongate projections 4, as shown in FIG. 3AFIG. 3B shows the bonded state of the IC chip 1 to the IC chip 2 shownin FIG. 3A.

[0041] As described above, since the bonding of the IC chip 1 to the ICchip 2 is largely dependent on the wedge effect utilizing the frictionbetween the two walls 3 a and 3 b of the tapered groove 3 and thetapered surfaces 4 a and 4 b of the elongate projection 4, together withthe force exerted in pinching the tapered surfaces 4 a and 4 b of theelongate projection 4 with the two walls 3 a and 3 b of the taperedgroove 3, it is possible to strengthen the whole bonding force byincreasing the area for substantially fitting the tapered groove 3 tothe elongate projection 4. Further, the total sum of the bonding forcesbased on the interatomic force and the metallic bond also increases withthe increase of the fitting area.

[0042] As shown in FIG. 3A, when the tapered grooves 3 are provided inrows at the same pitch throughout the bonding surface 1 a of the IC chip1, or when the tapered grooves 3, larger in number than that of theelongate projections 4, are provided in rows at the same pitch, the ICchip 1 may be bonded to the IC chip 2 with the tapered grooves 3 shiftedrelative to the elongate projections by some row pitches of the taperedgrooves 3.

[0043] Further, when both the accurate positioning and the strengthenedbonding force are required for the bonding of the IC chip 1 to the ICchip 2, the tapered grooves 3 and 5 differing in direction from eachother are respectively provided in rows on the bonding surface 1 a ofthe IC chip 1, while the elongate projections 4 and 6 respectivelycorresponding to the tapered grooves 3 and 5 are provided in rows on thebonding surface 2 a of the other IC chip 2, as shown in FIG. 4A

[0044]FIG. 4B shows the bonded state of the IC chip 1 to the IC chip 2shown in FIG. 4A.

[0045] In an embodiment shown in FIG. 4A, similarly to the embodimentshown in FIG. 3A, the IC chip 1 may be bonded to the IC chip 2 with thetapered grooves 3 shifted by some pitches relative to the elongateprojections 4. Further, since the bottom 5 a of the tapered groove 5adjacent to the end of the tapered groove 3 is formed to have a certaindegree of width, for example, a width equivalent to the sam of the otherseveral tapered grooves 5, unlike the width of each bottom of the otherV-shaped tapered grooves 5, the IC chip 1 can also be bonded to the ICchip 2 with the tapered grooves 5 shifted relative to the elongateprojections 6 by several pitches when bonding the IC chip 1 to the ICchip 2.

[0046] The number of pitches by which the tapered grooves 5 can beshifted relative to the elongate grooves 6, when bonding, is dependenton the relation between the row pitch of the tapered grooves 5 and thewidth of the bottom 5 a of the tapered groove 5 adjacent to the end ofthe tapered groove 3. For instance, when the width of the bottom 5 a isequivalent to three row pitches of the tapered grooves 5, the shift upto three row pitches is possible.

[0047] Even when the bottom 5 a of the tapered groove 5 adjacent to theend of the tapered groove 3 has the V-shape shape similar to that of thebottom of each of other tapered grooves 5, the same effect as the abovecan be attained as long as an appropriate gap is formed between theelongate projection 6 adjacent the end of the elongate projection 4 andthe end of the elongate projection 4.

[0048] Further, three or more IC chips can be bonded together by theapplication of various bonding methods shown in FIGS. 1A to 4B.

[0049] For instance, FIG. 5 shows an embodiment in which three or moreIC chips are bonded together in series by the application of the bondingmethod shown in FIGS. 2A and 2B.

[0050] In this case, since the IC chips are bonded together in series,both sides of each IC chip 7 serve as bonding surfaces 7 a and 7 b, andtapered grooves 8 and 10, differing in direction from each other, areformed on one bonding surface 7 a, while elongate projections 9 and 11respectively corresponding to the tapered grooves, 8 and 10 are formedon the other bonding surface 7 b. As shown in FIG. 5, the IC chips 7adjacent to each other may be bonded together, due to the wedge effectdescribed above, the interatomic force and the metallic bond, bybringing the bonding surface 7 a of one IC chip 7 into contact with thebonding surface 7 b of the other IC chip 7 and fitting the elongateprojections 9 and 11 on the bonding surface 7 b into the tapered grooves8 and 10 on the bonding surface 7 a.

[0051] In the embodiment shown in FIG. 5, the IC chips 7 of the exactlysame shape are bonded together in series. However, it is to beunderstood that as long as there is compatibility between the taperedgroove and the elongate projection on the bonding surfaces of theadjacent IC chips to be bonded together, the bonding of these IC chipsis possible, without causing any problems even if the adjacent IC chipsto be bonded together are different in size and shape.

[0052] Further, in the embodiment shown in FIG. 5, the tapered groovesare formed on one bonding surface of the IC chip, while the elongateprojections are formed on the other bonding surface of the same IC chip.However, it is to be understood that only the tapered grooves or theelongate projections may be formed on both of two bonding surfaces ofone IC chip, while the elongate projections or the tapered grooves maybe formed on the bonding surface of the other IC chip to be bondedthereto.

[0053] In the embodiment shown in FIG. 5, the bonding surfaces areprovided on both of the left and right sides of the IC chip for bondingthe IC chips together in series. However, it is to be understood thatthe bonding surface may be provided on each of two or more sidesarbitrarily selected from six sides of the IC chip so that three or moreIC chips can be bonded together in longitudinal or lateral rows or inlayers, or furthermore, in three-dimensional arrangements.

[0054] Since an aggregate of IC chips may be formed according to a spacefor the storage of the IC chips, space saving and higher integration ofa circuit can be made possible.

[0055] In the embodiments shown in FIGS. 1A to 5, an appropriate angleis required to be selected as a taper angle α of each set of the taperedgroove 3 and the elongate projection 4, the tapered groove 5 and theelongate projection 6, the tapered groove 8 and the elongate projection9 and the tapered groove 10 and the elongate projection 11 according tothe purpose of bonding the IC chips together.

[0056] If the undetachable bonding wherein one IC chip cannot bedetached from the other IC chip is desired, the taper angle α should beset to about 30° (Morse taper No. 0) as shown in FIG. 6A. On the otherhand, if it is desired that the IC chips bonded together can be keptbonded in the normal state but can be detached from each other withoutbreakage when an external force is applied, then, the taper angle αshould be set to about 3 to 90°, for example, about {fraction (7/24)}taper, as shown in FIG. 6B. Moreover, if only the simpleslidable-engagement is required, the taper angle α should be set to atleast 90° as shown in FIG. 6C.

[0057] As described above, although an adherent force (bonding force)caused by the interatomic force and the metallic bond is produced byfitting the elongate projections to the tapered grooves under pressure,the wedge effect produced by fitting the tapered grooves to the elongateprojections is the most influential factor of the bonding force, andtherefore, the strength of the bonding force can be adjusted by properlyselecting the taper angle α.

[0058] Further, in the positioning work where the elongate projectionsare fitted and pressed into the tapered grooves, the positioningaccuracy in the pressing direction, that is, the vertical directionshown in FIGS. 6A and 6B cannot always be assured accurately, and anuncut portion of about 10 nm in Rmax is sometimes left on the bottom ofthe tapered groove or the valley between the elongate projections afterthe formation of the tapered grooves and the elongate projections. Thus,it is necessary to form the bottom of each tapered groove and the end ofeach elongate projection in a trapezoidal form as shown in FIGS. 6A and6B, instead of a complete V-shape, so as to absorb the positioning errorin the pressing direction with a gap produced between the bottom of eachtapered groove and the end of each elongate projection and between thecrest defined by the adjacent tapered grooves and the valley defined bythe adjacent elongate projections.

[0059] Further, according to various bonding methods described withreference to FIGS. 1A to 5, the electrical connection between the ICchips can be done simultaneously with the bonding work to fit theelongate projections into the tapered grooves by providing an interfaceof each IC chip itself on the tapered groove or the elongate projectionformed on the bonding surface of the IC chip.

[0060]FIG. 7 shows an example of the configuration of the interface inthe case where IC chips of the rectangular parallelepiped shape arebonded together by fitting a pair of tapered groove and elongateprojection to each other.

[0061] In FIG. 7, only one of two IC chips to be bonded together, thatis, an IC chip 12 having a tapered groove 13 is shown, and thedescription relating to the other IC chip to be bonded thereto, that is,an IC chip having an elongate projection is omitted.

[0062] As shown in FIG. 7, a contact serving as the interface includes acontinuous belt-shaped contact like a contact 14 extending across thetapered surfaces 13 a and 13 b along the width direction of the taperedgroove 13, a short belt-shaped contact like a contact 15 provided on apart of the tapered surface 13a or 13b along the width direction of thetapered groove 13 and spot contacts 16 a, 16 b and 16 c each locallyprovided on the tapered surface 13 a or 13 b.

[0063] Further, contacts respectively corresponding to the contacts 14,15, 16 a, 16 b and 16 c are formed on the elongate projection formed onthe other IC chip to be bonded to the IC chip 12 in the manner similarto that in the case of the tapered groove 13 described above, and thecorresponding contacts are electrically connected to one another bybonding the elongate projection to the tapered groove 13 of the IC chip12 (not shown).

[0064] The belt-shaped contact like the contact 14 provided along thewidth direction of the groove may take a relatively large area forelectrical contact and therefore, is effective for stabilization ofconnection. Further, when spot contacts like the contacts 16 a, 16 b and16 c are provided in a row along the width direction of the taperedgroove 13 as shown in FIG. 7, the higher integration of the circuit canbe attained with ease, and also the length of te tapered groove 13 canbe reduced.

[0065] The interval between the contacts may be on the order of micronor sub-micron, similarly to the width or conductor spacing of the wiringproduced by the semiconductor process.

[0066] Described above is an example of the configuration of theinterface, in which the IC chips of the rectangular parallelepiped shapeare bonded together by fitting a pair of tapered groove and elongateprojection to each other. However, it is to be understood that theinterface utilizing the tapered groove and the elongate projection mayalso be applied to any of the embodiments shown in FIGS. 2 to 5,similarly to the embodiment shown in FIG. 7.

[0067] In particular, if the positioning accuracy in bonding the ICchips together is high, as in the cases of the embodiments shown inFIGS. 2A, 2B, 4 a and 4 b and 5, then the positioning accuracy of thecontacts serving as the interface of each IC chip is also high, so thatthe effective use of the contacts like the contacts 16 a, 16 b and 16 chaving small contact area is enabled, being advantageous in view ofhigher integration of the circuit.

[0068] In case of bonding the IC chips having a large number of taperedgrooves and a large number of elongate projections together, as in thecases of the embodiments shown in FIGS. 3a and 3 b, 4A and 4B, thenumber of contacts serving as the interface can be increased largely,being advantageous in view of higher integration of the circuit.

[0069] Further, in the embodiments shown in FIGS. 3a and 3 b, 4A and 4B,bonding work may be carried out with the elongate projections shiftedrelative to the tapered grooves by some pitches when bonding the ICchips together. Thus, as long as, a large number of contacts areprovided on each of the tapered grooves and the elongate projections, itis possible to change the state of electrical connection between the ICchips for easy modification of the entire circuit configuration only bysimply shifting the positions of engagement between the tapered groovesand the elongate projections from each other.

[0070] Further, since the contacts of the IC chips are directlyconnected together, the intermediate connecting means such as a leadframe, printed wiring and copper wiring becomes unnecessary, and, as aresult, it becomes possible to attain higher speed of the overallcircuit operation (i.e., shortening of the wiring). Besides, since noproblems relating to increase in the volume of the contacts or thewiring for connection arise, it is possible to attain higher integrationof the circuit.

[0071] In the foregoing, although a description has been given of thebonding of the IC chips as the embodiments of the bonding method of thepresent invention with reference to the accompanying drawings, it is tobe understood that the present invention is also applicable to bondingof small parts other than the IC chips, such as semiconductor partsincluding LSI or the like, semiconductor devices and micromachins.

[0072] For instance, the method of the present invention may be appliedto bonding of a bulk cache memory to a microprocessor. That is, abonding surface of the microprocessor is subjected to mirror finishing,a large number of V-shaped grooves are formed on the mirror-finishedbonding surface, and wall surfaces of these V-shaped grooves are alsosubjected to mirror finishing. On the other hand, a bonding surface ofthe bulk cache memory is also subjected to mirror finishing, a largenumber of V-shaped elongate projections are formed on themirror-finished bonding surface, and surface of these V-shaped elongateprojections are also subjected to mirror finishing. Then, the V-shapedelongate projections of the bulk cache memory are pressed into theV-shaped grooves of the microprocessor. In this case, since the surfacesof the V-shaped elongate projections and the wall surfaces of theV-shaped grooves are finished enough to provide highly-accurate surfaceroughness, the bulk cache memory and the microprocessor are bondedtogether by the action of the wedge effect and the interatomic force.

1. A bonding method of small parts, comprising the steps of: forming oneor two or more V-shaped grooves on a bonding surface of a first smallpart; forming a V-shaped elongate projection, which is engageable witheach V-shaped groove, on a bonding surface of a second small part; andbonding the first small part and the second small part together byfitting the V-shaped elongate projection of the second small part to theV-shaped groove of said first small part.
 2. A bonding method of smallparts according to claim 1, wherein the V-shaped grooves and theV-shaped elongate projections are formed respectively in rows inparallel arrangements on the bonding surface of said first small part.3. A bonding method of small parts according to claim 1, wherein a firstgroup of V-shaped grooves in rows in parallel arrangements and a secondgroup of V-shaped grooves in rows in parallel arrangements in adirection different from that of said first group of V-shaped groovesare formed on said first small part, and a first group of V-shapedelongate projections in rows in parallel arrangements and a second groupof V-shaped elongate projections in rows in parallel arrangements in adirection different from that of said first group of V-shaped elongateprojections are formed on the bonding surface of said second small partcorrespondingly to said first and second groups of V-shaped groovesformed on the bonding surface of said first small part.
 4. A bondingmethod of small parts according to claim 1, wherein an angle of saidV-shaped groove is set small and also bonding surfaces are finished withhigh accuracy so that the wedge effect and also the interatomic forceand the metallic bond may be produced between the first small part andthe second small part.
 5. A bonding method of small parts according toclaim 1, wherein an angle of said V-shaped groove is set slightly largerso that the parts may be kept bonded in the normal state but they can bedetached from each other when an external force is applied to them.
 6. Abonding method of small parts according to claim 1, wherein an angle ofsaid V-shaped groove is set so that said second small part may sliderelative to said first small part in the direction of the V-shapedgroove.
 7. A bonding method of small parts according to claim 1, whereinsaid V-shaped groove has a depth in the range from about 1 to 10microns.
 8. A bonding method of small parts according to claim 1,wherein said V-shaped groove is formed with anisotropic etchingtreatment using KOH.
 9. A bonding method of small parts according toclaim 1, wherein said V-shaped groove is machined by shaping or millingusing single crystalline diamond tool and a super-precision machine. 10.A bonding method of small parts according to claim 1, wherein said firstand second small parts are IC chips.
 11. A bonding method of small partsaccording to claim 1, wherein an electric contact for transfer ofsignals between said first and second small parts is provided on thebonding surface of said first small part and the bonding surface of saidsecond small part, and both the small parts are electrically connectedwhen both the small parts are bonded together by fitting the V-shapedelongate projection of said second small part to the V-shaped groove ofsaid first part.
 12. A bonding method of small parts according to claim1, wherein each of said first and second small parts is formed to have arectangular parallelepiped shape, and both the small parts are bondedtogether three-dimensionally in longitudinal, lateral and verticaldirections.
 13. A module of combined small parts, comprising: a firstsmall part having a bonding surface, on which one or two or moreV-shaped grooves are formed; and a second small part having a bondingsurface, on which one or two or more V-shaped elongate projections areformed; wherein the bonding surface of said first small part is bondedto the bonding surface of said second small part, with one or two ormore V-shaped grooves of said first small part engaged with one or twoor more V-shaped elongate projections of said second small part.
 14. Amodule of combined small parts, comprising: a first small part having abonding surface, on which a first group of V-shaped grooves in rows inparallel arrangements and a second group of V-shaped grooves in rows inparallel arrangements in a direction different from that of said firstgroup of V-shaped grooves are formed; and a second small part having abonding surface, on which a first group of V-shaped elongate projectionsin rows in parallel arrangements and a second group of V-shaped elongateprojections in rows in parallel arrangements in a direction differentfrom that of said first group of V-shaped elongate projections areformed correspondingly to said first and second groups of V-shapedgrooves formed on the bonding surface of said first small part; whereinthe bonding surface of said first small part is bonded to the bondingsurface of said second small part, with the V-shaped grooves of saidfirst small part engaged with said V-shaped elongate projections of saidsecond small part and also with said first small part positioned to saidsecond small part.
 15. A module of combined small parts, comprising: afirst small part having a bonding surface, on which one or two or moreV-shaped grooves are formed; and a second small part having a bondingsurface, on which one or two or more V-shaped elongate projections areformed; wherein at least one V-shaped groove of said first small parthas at least one contact formed on a part of oblique walls constitutingsaid V-shaped groove; at least one elongate projection of said secondsmall part has at least one contact formed on a part of oblique wallsconstituting said V-shaped elongate projection; the contact formed onsaid V-shaped groove and the contact formed on said V-shaped elongateprojection are brought into contact with each other, when the bondingsurface of said first small part is bonded to the bonding surface ofsaid second small part such that one or two or more V-shaped grooves ofsaid first small part and one or two or more V-shaped elongateprojections of said second small part are in engagement with each other.16. A module of combined small parts according to claim 15, whereincontacts are locally formed on a part of oblique walls constituting theV-shaped groove of said first small part.
 17. A module of combined smallparts according to claim 15, wherein a belt-like contact is formedextending from a part of each oblique wall constituting the V-shapedgroove of said first small part to a part of the bonding surfacecontinuous with the oblique wall
 18. A module of combined small partsaccording to any one of claims 13 to 17, wherein said first small partor said second small part is a semiconductor part.
 19. A module ofcombined small parts according to any one of claims 13 to 17, whereinsaid first small part or said second small part is a semiconductordevice.
 20. A module of combined small parts according to any one ofclaims 13 to 17, wherein said first small part or said second small partis a micromachine.